Method of firing blast furnaces



Patented Nov. 17,1942

curios METHOD OF FIRING BLAST FURNACES Lawrence E. Riddle, Duqucsne, Pa.

No Drawing. Application October 4, 1940,

Serial No. 359,797

4 Claims.

This invention relates toimproved methods of firing and more particularly relates to a method in which a substantial economy in time and materials is eflected in lighting up the blow-in burden in the case of s t 8. new, or retiring an extinguished, blast furnace.

When the improved method of firing is employed in connection with lighting up a furnace which has been banked and in which the fire has become extinguished, an employment of the tions of the readily combustible or highly combustible wood and charcoal. In accordance with the present invention, the initial charge of wood and charcoal are entirely dispensed with and it is possible, and has proven practicable, to readily eflect the initial firing by the use of coke alone.

In accordance with the usual custom of eflecting the initial lighting of the readily ignitable method enables an additional economy to be effected in time and labor by eliminating the necessity for completely cleaning out the remaining old charge comprising ash, refuse and other material in the furnace, including the slag, unburned fuel. and metal. The necessity for use of wood and charcoal in re-flring the furnace is also dispensed with. Further details in connection with the refiring of a banked blast furnace, in which'the fire has been extinguished, will be found fully considered in my co-pending application Serial No. 378,819, filed February 13, 1941, dealing with an improved method for banking a blast furnace.

In accordance with the practice'of the prior art, in a new furnace, or in the blast furnace that has been blown out, or one that has gone out from a long banking period, it has been common prac tice before the blow-in burden of coke, metal and limestone have been charged into the furnace, to

first put in a charge of wood, charcoal or other highly combustible and easily ignitable material which is supplied in the hearth or crucible part of the furnace at a point adjacent the tuyres. after which the wood and charcoal are ignited by blowing a flame or ignited material through the tuyeres and into contact with the wood or charcoal immediately adjacent the tuyeres, at the outer circumferential portion, of the wood or charcoal. The ignited material was usually insertedsometimes being blown-through the tuyere openings, the tapping hole, or iron-notch, which are openings in the circumferential wall and lining of the furnace. methods were not usually of such a character as permitted a control of the distribution of the zone of or degree of penetration of the initial ignition and combustion throughout the depth radially of the wood or charcoal, or which permitted various portions of the lowermost charge of' wood and/o1- charcoal to be ignited at a number of segregated portions at varying radial distancet along the axis of the combustion chamber of the furnace, but depended generally upon radiated heat, and a carrying of the flame, after a Such initial igniting and highly combustible wood or charcoal, the igniting flame is usually disposed, notwithin the hearth portion of the combustion chamber proper in intimate contact with the wood or charcoal, but is in the tuyres, and in some instances within a stove wholly outside of the wall oi the furnace, reliance being placed on the high temperature heat of a light air blast for carrying the igniting flame for the wood, within the furnace. By such an arrangement, no means are provided for obtaining a uniform and controlled distribution of the initial zone of ignition for starting or kindling fuel adjacent the tuyres at the bottom of th furnace, or of the depths or penetration of the initial ignition zone radially of the fuel charge, and along the axis of the chamber. The matter of obtaining initially a zone or'bed of combustion oi the fuel, uniformly distributed to varying depths throughout a horizontal "section of the furnace, is of considerable importance in the initial starting and also in the normal op- 'eration thereafter, particularly in the avoidance of certain irregularities of furnace operation due to non-uniformity of the fuel and charge disportion oi the wood was ignited, to other por- 55 tribution, resulting in a non-uniform zone or bed of combustion, causing channeling and chimneying eflects which result in conditions known as scaiiolding, pillaring, and the like, dependent upon the particular part of the combustion zone or bed at which the irregular or open spot, affording a path of least resistance, occurs.

One of the advantages in the employment of the present invention over prior customary practice of flrlngthe furnace is that by the elimination of the necessity for use of wood or charcoal, there'is avoided the usual and inevitable settling or dropping of the burden after the wood and charcoal have been burned.

A further advantage of the present invention over the prior customary practice, in the initial firing of the furnace, is that the likelihood of formation of carbon monoxide as a gas which finds its way to the flues or outlets of a furnace, and smoke, are minimized because of the conditions and control of the present invention, which are conducive to more complete combustion of the fuel' and gases formed therefrom. The formation of carbon monoxide and smoke are due to the incomplete combustion of the gas and. of the fine carbon particles which, after being formed, particularly on starting, are deposited in the upper portion of the furnace or are carried out in the flue. The reliance upon a diluted oxygen supply, such as that provided by the air, at the initial firing period, is conducive to the above conditions. A further hazard encountered at the starting period where air, as a diluted source of oxygen, is employed is the likelihood of formation of explosive mixtures because of the mixtures of furnace gas and air in a wide range of proportions. In prior practice, this has been a hazard requiring special care.

In accordance with the present method of operation, an undiluted source of oxygen is pro vided to assure substantially complete combustion of the coke, and means are'provided for controlling the points or portions of the bed of coke with which the substantially pure oxygen is brought into contact with the coke to facilitate complete combustion thereof. Such points inihas shown that the percentage of saving in fuel consumption effected by employing preheated air tially might be referred to as being initially segre gated portions at varying distances radially, and also circumferentialiy, disposed along the axis of the furnace combustionchamber, and particularly the lower hearth or crucible portion thereof adjacent the tuvres. When completecombustion of the coke is efiectedunder conditions in which air as a source of diluted oxygen supply is not used, the conditions are such as to greatly minimize the formation of poisonous carbon monoxide gases and the formation of wood smoke containing obnoxious gaseous compounds and also minimizes the possibility of explosions from mixtures of furnace gas and air in a wide range of proportions.

One of the advantages in utilizing undiluted or pure oxygen in firing a blast furnace as compared with using atmospheric air as a source of oxygen is that it is unnecessary to utilize the fuel .a uniform zone of combustion. At the startin period, the employment of 80% of the atmospheric air. as a non-oxidizing gas in an air blast would have a. cooling effect which would tend to defeat the purpose of rapidly initiating and maintaining a high temperature and rapid rate of combustion of the coke. .The atmosphere of unin blast furnace operation varies from around 12% to 70%, depending upon the temperature of the preheated air at the point of entry to the furnace, and the temperature of exit gases from the furnace. By not utilizing diluted oxygen such as in atmospheric air, it is possible to start the furnace with a higher ratio of ore to coke and thereby effect some fuel economy. Such data serve to indicate an advantage to be obtained in fuel economy in starting a new furnace, or re-firing a banked furnace in which combustion has become extinguished, by avoiding the necessity for use of any atmospheric air and by utilizing an atmosphere of undiluted oxygen, to t with a means for effecting a kindling temperature of the coke, at the initial starting period.

As illustrating one preferred manner in which the method of the present invention might be practiced, substantially pure or undiluted oxygen is employed for effecting substantially complete combustion of the coke. Means are provided for forming an atmosphere of undiluted oxygen at various portions of the coke bed .adjacentthe tuyeres and tapping hole of the combustion chamher in such a manner as to form, within a relatively short period after initially firing, a substantially uniformly distributed zone or bed of burning coke. After such a bed of burning fuel has been formed, the combustion of the fuel and subsequent operation of the furnace is carried on in the usual manner by employing the air blast to supply a diluted source of oxygen, such as atmospheric air, preferably preheated. Such air contains about 20% of oxygen.

In the practice of the method, satisfactory results have been obtained by employing oxygen lances which are metal steel tubes of considerable length, sometimes being from 10 to 15 ft.

, long, the ends of which are ignited and inserted diluted oxygen would greatly contribute to the rapid rate of combustion of the coke and would thus be conductive to the formation of heat by exothermic reaction when the undiluted oxygen combines with the carbon of the coke to form carbon dioxide;

The saving in fuel, by utilizing undiluted'oxygen and thus avoiding the necessity of having to heat a large volume of inert gas, is a substantial one. Experience has shown that in the operation of a blast furnace, a substantial percentage of saving in fuel consumption is effected by preheating the air. Such experience might be utilized as indicating a possible economy to be effected by avoiding the use of a large volume of inert gas-such as of the airand utilizing undiluted oxygen as a methodof facilitating initial kindling and combustion of the coke. Experience through the tuyres. In this manner, the source of igniting flame and the supply of substantially undiluted oxygen is carried in the combustion chamber, beyond the wall thereof, and is initially brought into intimate contact with various segregated portions of the bed of coke at various depths of the charge and at various points circumferentially along the axis. In this manner, there is a definite control made possible of the manner and disposition of initial ignition and combustion within the coke bed. The lances practically employed and found satisfactory included lengths of small A." steel pipe about 10 to 15 ft. long. It.

is, of course, understood that the specific structure, size, composition, and shape of the lances' may be widely varied to suit the various conditions of use.

It is also understood that the furnace may be provided with special apertures at various places to receive the oxygen lances and to facilitate the manipulation thereof in conducting the igniting flame and the undiluted oxygen directly to the points desired in penetrating the coke bed within a circumference defined by the walls of the combustion chamber, as distinguished from merely blowing a flame, together with a diluted source of oxygen supply through an aperture in the wall of such furnace. Preferably the starting coke should be of a size to be readily displaceable slightly, to permit penetration by the lances. Eoke from to 2" in size should be satisfac ory.

The present method is of particular value and importance when employed in re-flring a furmice which has been blown out, or which has been banked, and in .which combustion has been terminated. In accordance with prior practice,

charcoal, coke, ore, limestone and the like and re-ilre in the usual way. In accordance with the present invention, however, it has been found satisfactoryto apply wind to the tuyeres and blow out all possible ash through the tapping hole and cinder-notch, it not being necessary to remove the partially burned coke, ore, and other materials that remain in the furnace. After the removal of the ash and other refuse capable of being blown out in the manner above set forth, the methods of the present invention are employed for directly igniting the bed of coke which has settled in the bottom portion of the combustion chamber. It has been found in practice that when the method of the present invention is applied to the re-firing of a banked fumace in which combustion has been extinguished, a time saving of approximately six days is effected, considering a time from when the operation of removing the stock, called ravelling out, is begun until the furnace has been refilled and is ready to light or to be put in blast.

character of the initial product, obtained, the nature of the positive steps employed, resulting in the failure or omission to follow certain steps and customary practices of the prior art, are of such a character that it might fairly be said that the method was doing that which was deemed to be contrary to accepted customary practices in the art of banking and re-firing blast furnaces.

It is not possible at this time to state definite reactions, or a definite theory, or to give a positively accepted explanation of these improved results, in nature and uniformity of the product initially obtained, or of the saving in time after the initial firing, over the prior practices. However, the following might be mentioned in partial explanation as factors contributing toward the improved and unexpected results. By employing in the method a residue charge of coke and ore that has been dried out and previously subjected to the high heat of the blast furnace, such residue products, particularly the ore, are in a condition of partial refinement, different portions of the ore being in various states of reduction from that of substantially pure iron to different degrees or conditions of oxidation, including that The employment of the improved method of firing, herein disclosed, when employed with the improved method of banking, has been shown in actual practice to result in a saving of as much as six days as compared with the prior art prac tice and methods.

Inaddition to the elimination of various steps of ferrous oxide (FeO), hematite-ferric oxide (F820;) and magnetite (F8304) In this state of partial reduction of the residue charge, existing at the time that the furnace is banked in such manner as to preclude further combustion, it is perhaps possible that portions of the porous iron-withinzones of the blast furnace which of the prior art methods as heretofore practiced--1ive-banking and subsequent re-firing this method efiects a saving in time from the time of starting to the time of the initial tapping period. A comparison of the present method with those of the prior art, with respect to the period from the time of re-flring up to the time when an initial tapping of good iron may be obtained, has shown that by employing the residue charge of coke free from clinker and ash, and employing the undiluted source of oxygen, to sustain combustion, .the production of uniformly good iron on the initial tapping, can be obtained. in a much shorter period of time,

, than by the practice of prior method or customary practices, wherein the furnace was entirely cleaned out and another blow-in burden employed, where stock had been ravelled out, or in the case of live-banking where much of the coke had. been consumed and left great quantities of ash and clinker which could not be blown out.

It has also been found that by the employment of the method herein disclosed, the likelihood of the production of what is known as elf-grade iron is greatly lessened. In this respect, the practice of the improved method enables an improvement to be efiected in obtaining a greater uniformity in the grade and character of iron which is produced on the initial tapping following the firing of the furnace, and this in a shorter have been subjected to maximum temperatures of 450 degrees centigrade have absorbed certain amounts of free carbon, which has resulted from a reversible reaction between 200 oo,'+o+ss,sso calories 58,320 Calories 97,200 Calories This is an equilibrium reaction and the amount of carbon deposited depends upon the ratio of CO to CO2 and also upon the temperature-the period of time than by the practice of prior methods. .In this respect the resulting improvement in uniformity of the product on the initial tapping, obtained by the practice of this improved method, is striking and somewhat unex pected. The same statement might also be fairly made with respect to the saving in time within which the production of a uniformly good grade of iron upon initial tapping is obtained. Apart from the .unobvious improvement in the resulting maximum amount of carbon deposited being at about 450 degrees centigrade with This free carbon penetrates a porous ore to some extent and becomes a more powerful deoxidizer of the ore than C0, at temperatures above 750 degrees centigrade.

It is understood that a plurality of jets supplying the atmosphere of undiluted oxygen, together with ignition torches, may be disposed at various positions and depths of penetration of the coke charge and simultaneously fired, if desired, to initially obtain a bed or zone of combustion uniform in character.

While one preferred method has been disclosed, and certain apparatus referred to for the purpose of facilitating the practice of the method, it is of course understood that certain changes may be made in method of application and apparatus required, due to various conditions to be met with in use, and that such changes may be made withwhich includes the following steps: charging the furnace combustion chamber with the blow-in burden including iron ore. limestone andcoke but without wood or charcoal therein, and providing an atmosphere of substantially pure oxygen which is initially conducted to points within the combustion chamber in-intimate contact with segregated portions of the coke at varying distances radially and circumferentially along the axis of the combustion chamber, supplying a. flame source of heat at the points of delivery of the undiluted oxygen to the segregated coke portions to initially supply a localized zone of sufficiently high kindling temperature to facilitate initial kindling and combustion of the coke at such localized zones, withdrawing the supply of substantially undiluted oxygen after the coke is ignited, and supplying a light blast of air conducted to the combustion chamber from its walls for general diffusion therethrough and effusion through the coke, to continue the combustion of the coke throughout the furnace.

2. The improved method of re-firing a blast furnace having a charge of iron ore, limestone and coke without the use of any kindling wood or charcoal or any fuel other than coke, which includes the following steps: providing an atmosphere of substantially undiluted oxygen which is initially conducted to controlled and localized points within the combustion chamber in intimate contact with segregated portions of the coke at varying distances radially and circumferentially of the combustion chamber, supplying a kindling flame source of heat at the points of delivery of the undiluted oxygen to the segregated coke portions to initially supply a localized zone of sufiiciently high temperature to facilitate kindling and combustion of the coke, terminating the supply of substantially undiluted oxygen after the coke is ignited, and supplying a light blast of air to continue the combustion of the coke.

'3. The improved method of firing a blast furnace without the use of any combustible material, other than coke, which includes the following steps: charging the furnace combustion chamber with the blow-in burden of iron ore, limestone and coke sized from approximately three-quarters of an inch to two inches but without wood or charcoal therein, and providing an atmosphere of substantially undiluted oxygen, which is initially 7 of the coke by inserting oxygen lances through various tuyres, openings and the tapping hole of the furnace so as to extend therein at difl'erent depths in contact with the coke therein, supplying a controlled and localized flame source of kindling heat at the points of delivery of the undiluted oxygen to the segregated coke portions to initially supply a localized kindling zone of sufllciently high temperature to facilitate combustion of the coke, withdrawing the oxygen lances after a substantial number of the segregated portions of the coke have been kindled to form a substantially uniform bed of ignited coke, and supp ying a light blast ofa diluted source of oxygento continue the combustion of the coke.

4. The improved method'of re-firing a blast furnace having an extinguished charge of partly reduced iron ore, limestone and coke, without the use of any wood or charcoal or any fuel other than coke and without the necessity of cleaning out the entire furnace and inserting a fresh burden of iron ore, limestone, coke and kindling wood or charcoal, which includes the following steps: opening the tap hole and cinder-notch of the furnace, applying a blast of air to th tuyres to blow out the ash and the like, providing an atmosphere of substantially undiluted oxygen which is initially conducted to controlled and localized points within the combustion chamber in intimate contact with segregated portions of the coke by inserting oxygen lances through various tuyre openings and the tapping hole of the furnace, so'as to extend therein at different depths in contact with the coke therein, supplying a flame source of kindling heat at the points vof delivery oi the undiluted oxygen to the segregated coke portions to initially supply a localized zone of sufliciently high temperature to facilitate kindling and combustion of the coke, withdrawing the oxygen lances after a substantial number of the segregated portions of the coke have been ignited to form a substantially uniform bed of ignited coke, and supplying a light volume of air LAWRENCE E. RIDDLE. 

